Large enterprises and content providers, who depend on the Internet to operate their businesses, require a high level of reliability from their network connections. Increasingly, these large consumers and producers of network data are turning to multi-homing as a technique to achieve resilience to service interruptions. Multi-homing is defined simply as a customer (or Internet Service Provider [“ISP”]) network having more than one external link, either to a single ISP, or to different providers. The customer typically has its own public Autonomous System (“AS”) number, and advertises its address prefixes via all of its upstream providers using Border Gateway Protocol (“BGP”). See BGP4: Inter-Domain Routing in the Internet by John W. Stewart, Addison-Wesley Pub. Co. (1st ed. 1998) or Internet Engineering Task Force (IETF) Request for Comments (RFC) 1771, for a general discussion of the Border Gateway Protocol.
While multi-homing to multiple providers is motivated primarily by a need for link-level and provider-level fault tolerance, recently developed “intelligent route control” devices and services allow subscribers to leverage multi-homing for more than just increased resilience. For example, performance to different parts of the network may vary depending on which upstream provider is used. In such situations, careful route selection can significantly improve performance. Even availability can be managed to some extent by choosing ISPs that have sufficiently diverse connectivity to destinations of interest.
Route control solutions require two main components: measurement of the candidate links, and control to steer outgoing traffic over the best performing link. The measurement component typically measures the delay and loss over upstream provider links to various destinations in the network. Using these measurements, the best provider to reach a particular destination can be identified. Once the best provider is identified, however, traffic to the destination must be directed over the appropriate link. Current solutions achieve this link/ISP selection by interacting with the BGP router(s) connecting the data center to the ISP, usually with an external device adjunct to the router making this selection.
Current solutions are implemented as network appliances deployed in data center or enterprise networks. These appliances typically measure delays and availability over each ISP link using passive and active probing techniques such as observing Transmission Control Protocol (“TCP”) connection establishment delay, or using network pings. These low-level measurements are not application-specific, which means that the delay measurements must be translated into a metric that is meaningful for the application communicating over the network. In the currently available solutions, route control is done by modifying BGP forwarding tables so that traffic destined for a particular network uses the best-performing ISP based on observed performance. This requires installation of the appliance near the edge routers in the network, and complex router configuration to allow the appliance to direct traffic over links that may be contrary to the choice made by the standard BGP protocol.